Side-chain functional groups, glass

Pseudopoly(amino acids) are polymers derived fi om amino acids with nonamide linkages these are represented by the wavy line in Structures 20,21, and 22. This is usually done by the polymerization of trifunctional amino acids by reaction with side chain functional groups. Three important categories include serine derived polyesters [88] hydroxy-proline derived polyesters, and tyrosine-derived polymers. The first has not been widely used as a biomaterial [89]. The second group consists of poly(A-acyl-hydroxyproline esters) from A-protected hydroxyproline. These polyesters are soluble in benzene, toluene, chloroform, di-chloromethane, carbon tetrachloride, tetrahydrofuran, and dime thy Iformamide. They are thermally stable up to 300 °C, have glass transition temperatures ranging firom 71 °C to 157 °C, and are easily processed [89]. 

Other immobilization methods are based on chemical and physical binding to soHd supports, eg, polysaccharides, polymers, glass, and other chemically and physically stable materials, which are usually modified with functional groups such as amine, carboxy, epoxy, phenyl, or alkane to enable covalent coupling to amino acid side chains on the enzyme surface. These supports may be macroporous, with pore diameters in the range 30—300 nm, to facihtate accommodation of enzyme within a support particle. Ionic and nonionic adsorption to macroporous supports is a gentle, simple, and often efficient method. Use of powdered enzyme, or enzyme precipitated on inert supports, may be adequate for use in nonaqueous media. Entrapment in polysaccharide/polymer gels is used for both cells and isolated enzymes. 

Finally, it should be mentioned that often solids are more desirable than liquids in typical applications of films. The prospects for obtaining polymer films with useful thermodynamically stable %(2) seems high given the recent demonstration that functional group orientation in FLC side chain polymers appears very similar to that observed for the low molecular weight materials (IQ). The fact that FLC polymers possess thermodynamically stable polar order in a non-crystalline solid film would appear to make this novel type of polymer glass uniquely suited for many second order NLO applications. 

Photophysical and photochemical processes in polymer solids are extremely important in that they relate directly to the functions of photoresists and other molecular functional devices. These processes are influenced significantly by the molecular structure of the polymer matrix and its motion. As already discussed in Section 2.1.3, the reactivity of functional groups in polymer solids changes markedly at the glass transition temperature (Tg) of the matrix. Their reactivity is also affected by the / transition temperature, Tp, which corresponds to the relaxation of local motion modes of the main chain and by Ty, the temperature corresponding to the onset of side chain rotation. These transition temperatures can be detected also by other experimental techniques, such as dynamic viscoelasticity measurements, dielectric dispersion, and NMR spectroscopy. The values obtained depend on the frequency of the measurement. Since photochemical and photophysical parameters are measures of the motion of a polymer chain, they provide means to estimate experimentally the values of Tp and Tr. In homogeneous solids, reactions are related to the free volume distribution. This important theoretical parameter can be discussed on the basis of photophysical processes. 

---